Anomalisa is co-directed by Kaufman with Duke Johnson, who makes stop-motion animation. Directors habitually worry about the so-called "uncanny valley", that effect of CGI that looks almost real but not quite not real enough. With Anomalisa, Kaufman and Johnson move into Uncanny Valley and pull up the drawbridge: it looks very odd. It also sounds odd. Everyone except the two main characters is voiced with eerie blandness by the actor Tom Noonan. Michael is voiced by David Thewlis; Jennifer Jason Leigh plays Lisa, the only person Michael perceives as different from everyone else, his "anomaly".

And now here we are with Kaufman, who doesn't want to explain anything. Actually, he doesn't need to. Everything he wants to say is in the films; you just need to join the dots. I give it a go.

So, where does it all come from? "I don't have a lot of inspiration," Kaufman sighs. "I mostly just sit there and worry that I don't have any inspiration. That is really what I do. I mostly can't write if that is what you are asking. I struggle to do it. There are no set hours … I worry, especially if I'm working on something. I worry for years, sometimes. But non-stop."

I think we knew that. Remember the writer also called "Charlie Kaufman" in Adaptation, who can't seem to get past the fact he's writing a script "about flowers". Think of the director in Synecdoche, New York who keeps building rooms on to his theatre to house scenes from the play/life that will never be finished. Until he is finished, of course, which happens to us all. Death! The briefness of our span is always in there somewhere. Look at the desiccated group of elderly in Being John Malkovich, preparing to move en masse into Malkovich's mind. They want to live forever – but they are also dying to die.

Who are these people? In Anomalisa, the puppets representing Michael and Lisa are modelled on real people: Michael on Duke Johnson's brother-in-law; Lisa on a woman the directors scouted in a restaurant in an informal casting. "We didn't want them to look like the actors who were playing them," says Kaufman. "I think it then becomes like a stunt and it takes you out of the story. You see it a lot in big-budget animations … where you go 'oh yeah OK, it's Chris Rock!'"

But it's not just about letting the work stand alone. The fluidity – or terrifying uncertainty – of identity is central to Kaufman's films. From those wannabe John Malkoviches to the humans surging with animal lusts in Human Nature to the actors playing other actors playing themselves in Synecdoche, New York, nobody is a fixed entity. And what is an entity, anyway? Just a fleshy carapace containing memories – which, as in Eternal Sunshine, can be neatly erased.

And what's it all for? "I think we are all stuck in our bodies, stuck in our lives, stuck in our situations, you know. Stuck in the world. I think that's true," Kaufman says as he gets up to escape into San Sebastian's network of bars. A man could get lost in there forever, which is possibly what he would like right now. As for being stuck in our situations: that's Kate Winslet in Eternal Sunshine, forever doomed to fall in love, get bored and leave the same man, over and over again. Something similar happens to Michael in Anomalisa, but I won't ruin it with explanations. As Kaufman advises, you can see it and work it out for yourself.